Hybrid Single-Walled Carbon Nanotube-Nanocellulose Networks as Current-Collector-Free Electrodes

Hybrid nanoarchitectures that combine structural functionality of nanocellulose (NC) with electrical conductivity of carbon nanotubes (CNTs) are of growing interest for electroanalytical electrode design. However, CNT:NC hybrid film electrodes reported to date typically rely on separate conductive substrates, require binders, and rarely establish systematic relationships between processing, structure, and electrochemical performance. Here, we develop intrinsically conductive hybrid electrodes with a straightforward design, comprising current-collector-free, binder-free active layer from long-length single-wall carbon nanotubes (LLSWCNTs) and TEMPO-oxidized cellulose nanofibers (TOCNFs), fabricated on insulating support. To evaluate the influence of composition and processing parameters, films were prepared at three LLSWCNTs:TOCNFs mass ratios (1:1, 2:1, 3:1) and three postmixing sonication times (5, 10, 30 min). The films were subsequently characterized in terms of their structure, interfacial chemistry, and electroanalytical performance. Noncovalent interactions produced interconnected conductive LLSWCNTs networks embedded within an insulating TOCNFs scaffold, where electrical transport occurs through percolating interbundle contacts. Increasing LLSWCNTs content enhanced conductivity but densified the network, revealing a composition-dependent trade-off between charge and mass transfer. Extending postmixing reduced surface roughness and improved network homogeneity and charge-transfer kinetics. Electrochemical measurements demonstrated efficient outer-sphere electron transfer (k0 ∼ 0.4 × 10-2 cm s-1), a large electrochemically active surface area (ECSA = 0.053 ± 0.003 cm2), a wide potential window (ΔE = 2.41 ± 0.35 V in PBS), and significant pseudocapacitance (Cpseudo = 58.9 ± 7.7 μF cm-2), consistent with highly accessible porous electrode structures based on current collectors' substrates. This work provides design guidelines for fabricating aqueous-processed nanostructured hybrid electrochemical sensors.